As thin and flat large display in recent years, attention has been paid to a plasma display panel (referred to hereinafter a “PDP”) together with a liquid crystal display. A part of PDP has a structure wherein a dielectric layer consisting of sintered glass is formed on the surface of a glass substrate having an electrode fixed therein.
A method of forming this dielectric layer wherein a paste composition containing glass powder, an acrylate-based resin and a solvent is applied onto a support film to form a film-forming material layer, then the film-forming material layer formed on the support film is transferred onto the surface of a glass substrate having an electrode fixed therein, and the transferred film-forming material layer is sintered to form a dielectric layer on the surface of the glass substrate is disclosed (see JP-A 9-102273 and JP-A 2001-185024).
As the dielectric layer-forming resin composition, a composition comprising 100 to 500 parts by weight of dielectric inorganic powder added to 100 parts by weight of a self-adhesive resin having a weight-average molecular weight of 20,000 to 1,000,000 and a glass transition temperature of 15° C. or less obtained by copolymerizing 80 to 100% by weight of C1 to C12 methacrylate with 0 to 20% by weight of another monomer copolymerizable therewith is disclosed (JP-A 11-35780 and International Patent Publication No. 00/42622).
A transfer sheet having at least a base film and a transfer layer arranged in a releasable manner on the base film, wherein the transfer layer comprises at least a glass frit-containing inorganic component and an organic component capable of removal upon sintering and has surface smoothness Ra in the range of 0.4 μm or less, is disclosed (JP-A 11-260254). It is described therein that the organic component can, if necessary, contain a transferability-conferring agent such as ortho-phosphates etc. and a dispersant and suspending agent such as a phosphate based-surfactant etc.
However, the conventional paste composition or dielectric layer-forming resin composition has a problem that in a step of sintering a transferred film-forming material layer to form a dielectric layer, the light transmittance of the dielectric layer is reduced due to bubbles occurring and remaining in a melted film-forming material layer. Particularly in sintering in the low-temperature range in which the corrosion of an electrode or the deformation of a substrate does not occur by heating, the bubbles occurring in the melted film-forming material layer are hardly removable, thus significantly reducing the light transmittance of the dielectric layer. The dielectric layer is required to have high surface smoothness for use in a display, but the conventional paste composition has high viscosity upon melting, and thus there is a problem that the traces of bubbles occurring in the melted film-forming material layer remain as such, to deteriorate the surface smoothness of the dielectric layer. In the dielectric layer formed on a front plate of PDP particularly required to have transparency, there is demand for solving the problems of light transmittance and surface smoothness.
It is described in JP-A 11-260254 supra that phosphates may be added if necessary for the purpose of improvement of the dispersibility and suspending ability of inorganic powder and improvement of transferability and composition flowability, but not added for the purpose of improvement of the light transmittance of the dielectric layer. Further, there is no description of a specific example showing the effect of phosphates added.